Method of manufacturing a lead for an active implantable medical device with a chip for electrode multiplexing

ABSTRACT

A method of manufacturing a lead. The method includes providing a supporting tube, and disposing a conductive strip on an outer surface of the supporting tube such that the conductive strip extends in an axial direction along a length of the supporting tube. The method also includes mounting a chip having a first conductive contact pad and a second conductive contact pad to the supporting tube such that the first conductive contact pad is in contact with the conductive strip. The method further includes fitting an electrode to the supporting tube such that the electrode is in contact with the second conductive contact pad, and coupling a conductor to each end of the supporting tube such that each conductor is in contact with the conductive strip. The method also includes covering at least one of the chip and the conductors with a sheath to provide the lead.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/696,064, filed Apr. 24, 2015, which is a continuation of U.S.application Ser. No. 13/325,930, filed Dec. 14, 2011, which claims thebenefit of and priority to French Application No. 1060452, filed Dec.14, 2010, which are hereby incorporated by reference herein in theirentireties.

BACKGROUND

The present invention relates to “medical devices” as defined by the 14Jun. 1993 Directive 93/42/CE of the Council of the European Communities,and more particularly to “active implantable medical devices” as definedby the 20 Jun. 1990 Directive 90/385/EEC of the Council of the EuropeanCommunities, including those devices that continuously monitor apatient's heart rhythm and deliver to the heart, if necessary,electrical pulses for stimulation, resynchronization, cardioversionand/or of defibrillation, as well as neurological devices, drug deliverysystems, cochlear implants, implantable biological sensors, and similardevices, and as well as devices for measuring pH or intracorporealimpedance (such as the trans-pulmonary impedance or the intracardiacimpedance).

For the collection or detection (the terms being used interchangeablyherein) of signals, and for the delivery of pulses for stimulation, suchas for cardiac pacing, active implantable medical devices use electrodesthat are incorporated into a lead that is connected to the generator ofthe device. The generator contains the signal collection circuits andthe pulse generator circuits. The electrodes are intended to come intocontact with the tissues from which an electrical signal is to becollected, and the tissues to be stimulated, such as the myocardium,nerve, or muscle tissues, as the case may be. In the case of a devicefor cardiac diagnosis and therapy, these electrodes can be endocardial(placed in a cavity of the myocardium in contact with the wall of themyocardium), epicardial (placed on an outside wall of the myocardium, inparticular to define a reference potential, or to apply a shock) orintravascular (implanted, for example, in the coronary sinus artery to alocation opposing the wall of the left ventricle).

A first aspect of the development of these active implantable devices isthe increasing number of electrodes, particularly for those devicescalled “multisite” devices, that allow for choosing between differentstimulation/detection sites and optimizing the operation of the device.The increasing number of electrodes can also result from the presence ata same level of the lead of several sector electrodes (which areelectrodes specifically directed in a radial direction with respect tothe lead, at the stimulation site), with the option to select one oranother of these sector electrodes to optimize the delivery of pulses tothe selected site. This is particularly true for leads implanted in thecoronary venous system, for indirect stimulation of a left cavity: withseveral sector electrodes, it is relatively easy to choose the one thatfaces the wall of the epicardium in front of the cavity and in contactwith the wall and thus to avoid phrenic nerve stimulation.

Another aspect of the development of implantable devices is theintegration of different sensors into the lead, especially bloodpressure or acceleration sensors, including endocardial acceleration(EA) sensors. The signals collected by these sensors provide informationrepresentative of the instantaneous hemodynamic status of the patient,allowing for more effective control of the various functions of thedevice.

These lead sensors also require a specific connection for thetransmission of signals from the sensor, typically located at the distalend of the lead, to the generator connected at the opposite, proximalend. This connection is specific to the sensor and is superimposed onthe specific connections existing between the generator and the variouselectrodes located in the distal region of the lead.

In any case, to accommodate as many conductors as there are electrodeswould lead to both unacceptable dimensions for the lead and difficultiesin manufacturing the lead, especially at the connecting link between thelead at its proximal end and the implantable generator to which it iscoupled.

These developments, therefore, require the introduction of multiplexingelectronic circuits to manage the exchange of multiple signals betweenthe lead (electrodes and/or sensors) and the generator, and vice versa.Multiplexing is provided in situ, close to the electrodes by anelectronic circuit (hereinafter simply called “chip”) embedded in thedistal part of the lead, at or in the vicinity of its end (wherein thesignals are collected and/or the pulses are to be delivered).

The EP 1938861 A1 (US counterpart: US2008/0177343) and EP 2082684 A1 (UScounterpart: US2009/0192572) (all commonly owned by Sorin CRM S.A.S,previously known as ELA Medical, of Clamart France) describe such a leadhaving a plurality of electrodes, for example, ten electrodes, near itsdistal end associated with a chip, hermetically encapsulated in thevicinity of the electrodes in a rigid ring, providing themultiplexing/demultiplexing of the electrodes with a common bus formedby two insulated conductors extending along the entire length of thelead to the proximal connector, allowing the coupling with thegenerator, the latter being equipped with a counterpartdemultiplexing/multiplexing circuit.

WO2010/091435 A2 and WO 2006/069322 A2 (Proteus Biomedical, Inc.)describe a system in which a common two-wire bus transmits signalsfrom/to sector-addressable electrodes formed on “satellites” located onthe lead at regular intervals. A multiplexing/demultiplexing chip ismounted inside the lead, and connected to the wires of the bus by meansof welded micro-springs. The construction described, however, onlyleaves the lead with an internal lumen having a very small internaldiameter relative to its outside diameter, due to the size of the chipand connections to the wires. This constraint limits the application ofthis technique to electrodes located at the distal end of lead, becausethe small lumen diameter would not allow the use of traditionaltechniques of implantation, unless by greatly increasing the outerdiameter of the lead at the location of the those distal electrodes,which would in turn limit the applications. In addition, theimplementation technology is extremely difficult to implement and itsreliability over time has not been proven.

SUMMARY

It is, therefore, an object of the present invention to provide a leadhaving an internal lumen with a diameter comparable to that of thecurrently existing leads (typically having an inner diameter of 0.55 mmor 1.65 French), and electrical insulation over conductors and the chip.

It is another object of the present invention to provide a such leadwith an outer diameter comparable to currently existing leads (typicallyan external diameter of 1.6 mm or 4.8 French or even 4 French), with arelatively constant diameter along the length of the lead, namely a leadconfiguration known as “monodiameter.”

It is a further object of the present invention to provide such a leadwith a chip natively encapsulated thanks to the geometry andconfiguration of the elements of the lead, with excellent electricalinsulation and mechanical protection against both torsional stress andbending.

The present invention is directed to a lead of the above known type, forexample as disclosed in the WO 2010/091435 A2 cited above, comprising:an elongated flexible sheath with a central lumen; at least oneconductive connection housed in the lumen of the sheath; a rigidcylindrical supporting tube in an isolating material, with a crossingcentral bore, the supporting tube being interposed in the sheath,namely, being inserted in the sheath so that its crossing bore iscoaxial (i.e., in axial alignment) with the lumen of the sheath, thesupporting tube including in its surface a cavity forming a receptaclefor a chip, opening into a central region of the supporting tube; atleast one electrode provided on the sheath surface; and at least oneelectronic circuit on a substrate comprising a chip, and at least twoconductive pads respectively connected to the conductive connection andto the electrode, the chip having an outer conductive pad on one side ofthe substrate and on the opposite side an inner conductive pad, theelectrode being electrically connected to the outer conductive pad ofthe chip; and a feedthrough conductor connected in a central region tothe inner conductive pad of the chip.

Preferably, the substrate of the chip is a flexible substrate, disposedwith a curved conformation in the receptacle of the supporting tube. Inone embodiment, the conductive connection housed by the sheath includesa disconnect at the supporting tube location, and the feedthroughconductor is a conductive strip formed at the surface of the supportingtube, extending in the axial direction throughout the supporting tube,and connected at both ends face-to-face with the conductive connectionhoused in the sheath. Preferably, the electrode is for signal collectionand/or pulse delivery, and more particularly is for cardiacsensing/pacing.

In another embodiment, the chip has a flexible substrate with an outerconductive area on one side of the substrate and an inner conductive padon the opposite side, and is disposed with a bent conformation in thereceptacle of the supporting tube. Preferably, a sensing/pacingelectrode is carried by the supporting tube and is electricallyconnected to the exterior conductive pad of the chip. As for theconductive strip, it is preferably connected (i) at each end face toface to the conductive connection(s) housed in the sheath, and (ii) in acentral region, to the inner conductive area of the chip.

In one embodiment, the insulating material of the supporting tube is aceramic. Preferably, the lead has a unique ring electrode the shape ofwhich is a conductive sleeve circumferentially extending around theentire periphery of the supporting tube and slipped over the centralregion of the supporting tube.

In one embodiment, the lead has a plurality of sector electrodesisolated from each other, circumferentially distributed around theperimeter of the supporting tube and each connected to a correspondingplurality of conductive pads outside of the chip.

Preferably, the overall diameter of the lead is essentially constant inthe region of the supporting tube and of the electrode, and equal to thediameter of the flexible sheath.

In a preferred embodiment, the lead has two separate conductiveconnections housed in the lumen of the sheath, the supporting tubeincluding two corresponding crossing separate conductive strips that areisolated from each other and more preferably formed in diametricallyopposed regions on the surface of the supporting tube.

Advantageously, the present invention results in a lead offering thepractitioner a conventional lead configuration, allowing for itsimplantation using, and without changing, the normal implantationtechniques. Also advantageously, the present invention provides a leadthat can be manufactured by implementation of standard processes in themanufacture of leads, that is to say proven processes that can beimplemented at lower cost.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, characteristics, and advantages of the presentinvention will become apparent to a person of ordinary skill in the artfrom the following detailed description of embodiments of the presentinvention, made with reference to the annexed drawings, in which likereference characters refer to like elements, and in which:

FIGS. 1-8 show the successive steps for manufacturing the section of afirst embodiment of the lead including the chip and at least oneelectrode, with its various components, according to the presentinvention, with FIG. 1 illustrating a supporting tube before receiving aflexible chip, FIG. 2 illustrating a partial cutaway view of thesupporting tube of FIG. 1 , FIG. 3 illustrating a partial cutaway viewof the supporting tube of FIG. 2 after installation of a flexible chip,FIG. 4 illustrating the supporting tube of FIG. 3 after installation ofa conductive sleeve, FIG. 5 illustrating the supporting tube of FIG. 4after sealing the assembly against the external environment, FIGS. 6 and7 illustrating the supporting tube of FIG. 5 after being welded to theconductive connection, and FIG. 8 showing a cut-away view of therelevant portion of the lead in its finished state; and

FIGS. 9 to 11 show the successive steps for manufacturing the section ofa second embodiment of the lead including the chip and several sectorelectrodes, in which FIG. 9 illustrates a supporting tube for supportinga sector electrode, FIG. 10 illustrates the supporting tube of FIG. 9after installation of an insulating sleeve, and FIG. 11 illustrates thesupporting tube of FIG. 10 after installation of the sector electrodes.

DETAILED DESCRIPTION

With reference to the drawings, preferred embodiments of the presentinvention will now be described.

With reference to FIG. 8 , a portion of a lead in accordance with afirst embodiment of the present invention is illustrated with itsvarious components, as obtained after execution of the variousmanufacturing steps illustrated in FIGS. 1 to 7 . Reference 10 generallydesignates the body of a known lead used for cardiacdetection/stimulation, for which only a portion is shown (FIGS. 1-8 ),which portion is generally located near the distal end, including amelectrode, e.g., a detection and/or stimulation electrode. The electrodeis illustrated as an annular electrode in the first embodiment shown inFIGS. 1-8 . The electrode is illustrated as a plurality of sectorelectrodes in the second embodiment shown FIGS. 9-11 (described furtherbelow).

Lead 10 also includes two conductive connections in the form ofindividually isolated coiled wires, each of the two connectionspreferably being, for example, a respective pair of conductors 12, 12and 14, 14. These conductive connections run along the entire length ofthe lead and are connected at the proximal end of the lead to a couplingconnector to a generator implant (not shown). Lead 10 also carries aring electrode 16 connected to a chip 18 providing themultiplexing/demultiplexing functions (as well as to other electrodeslocated in other parts of the lead) with conductive connections 12, 14acting as a connection bus between the various electrodes of lead 10 anda remote generator (not shown).

Chip 18 is electrically connected, on the one hand, to electrode 16 and,the other hand, to each of conductive connections 12 and 14.

For convenience and simplicity of the description of a preferredembodiment of the present invention, chip 18 is described here as amultiplexer/demultiplexer of electrode(s), but a person of ordinaryskill in the art would understand that the present invention is notlimited to this exemplary type of circuit and that chip 18 also or inthe alternative may be coupled to a sensor (e.g., a signal transducerthat produces an electrical signal representative of the changes of aphysical parameter being monitored by the sensor). In this regard, inone embodiment chip 18 may incorporate such a sensor, or include anactive electronic circuit such as an amplifier, or filter, with orwithout a sensor placed nearby, or a micro-electromechanical (MEMS)device, or generally, any active element that may be technologicallyintegrated into a lead body. As contrasted with the structure andelectrical interconnections, the multiplexing/demultiplexing, switching,and any signal processing functions of chip 18 form no part of thepresent inventions.

Chip 18 in this embodiment has two outputs corresponding to conductiveconnections 12 and 14 of the wire bus, and a third output for connectionto electrode 16, and possibly additional outputs in the case, forexample, of a multi-electrode configuration (as in the case of FIGS. 9to 11 described below, comprising a plurality of sector electrodesmultiplexed by a single chip).

Preferably, chip 18 is mounted on a rigid cylindrical supporting tube 20made of an insulating material and having a central crossing bore 22ensuring, with no reduction in diameter, the continuity of the innerlumen of the lead, necessary, for example, for the passage of a styletor a grommet during an implantation procedure (see FIGS. 1 and 3 ).

To allow mounting on the cylindrical supporting tube, chip 18 preferablyhas a flexible substrate, meaning that the substrate is thin enough tobe bent and to fit to the cylindrical surface of the substrate. Thistechnique is, for example, described by Zimmermann et al., A SeamlessUltra-Thin Chip Fabrication and Assembly Process, Electron DevicesMeeting IEDM '06, 11-13 Dec. 2006, pp. 1-3, to which one skilled in theart is referred and which disclosure is hereby incorporated herein byreference. To make chip 18 flexible, it is necessary to thin thesubstrate (usually a silicon substrate) to a thickness of less than 0.1mm, so that it can match the shape of tube 20, whose outside diameteris, in the illustrated example, 0.85 mm, where chip 18 is located.

With particular reference to FIG. 3 , chip 18 has on an outer (convex)surface on which is located an outer conductive pad 24. Pad 24 isintended to come into contact with electrode 16 (see FIG. 8 ), and itcarries at its opposite (concave) outer surface two internaldiametrically opposed conductive pads 26 (only one of pads 26 is visiblein the FIGS. 3, 4, and 6-8 ), intended to be connected, as describedbelow, respectively to conductive connections 12 and 14. These variousconductive pads comprise, for example, an alloy of gold that can besoldered by reflow at 450° C. to establish the electrical connectionsrequired with the elements just mentioned.

FIGS. 1 and 2 show, separately, supporting tube 20 before it receivesflexible chip 18 (FIG. 2 is a cutaway view of FIG. 1 showing in sectionthe internal structure of the tube). Tube 20 is a tube made of anelectrically insulating material, preferably constructed by overmoldingplastic or ceramic components assembled together by high temperaturereflow or by gluing. It has two elongated conductive strips 28,preferably diametrically opposed (one of these strips is visible in thefigures) formed on the surface and extending in an axial direction alongmost of the length of tube 20 to form a crossing, with an apparentcentral region 28 a and two end regions 28 b.

Supporting tube 20 comprises a central region 30 of a greater diameter,e.g., 1 mm in the example shown, provided in its surface with a cavity32 forming a receptacle for flexible chip 18. The depth of cavity 32substantially corresponds to the thickness of chip 18 so that once chip18 is established in cavity 32, it is essentially flush with the contourof cavity 32 (as shown in FIG. 3 ). The configuration of tube 20 is suchthat central part 28 a of crossing strip 28 is visible, i.e., exposed,at the bottom of cavity 32.

Supporting tube 20 also has two end regions 34 of a smaller diameter,e.g., 0.85 mm in the example shown, with two respective ends 28 b ofcrossing conductive strip 28. The length of tube 20 is, in this example,about 5 mm and the surface area of cavity 32 is about 1 to 2 mm²

It should be understood that central bore 22 is completely electricallyisolated from crossing strips 28 and from cavity 32, with a wallthickness 36 (as shown in FIG. 2 ) of supporting tube 20 of about 0.55mm. This structure helps maintain the electrical isolation whilemaintaining a relatively large bore diameter.

FIG. 3 illustrates the supporting tube after installation of chip 18 incavity 32.

The next step in the manufacturing process, illustrated in FIG. 4 , isto put on the assembly a previously obtained sleeve 38 made of aconductive material, fitted to central region 30 of supporting tube 20and based on the full extent in the axial direction of cavity 32, sothat sleeve 38 covers the entire surface of chip 18. A thermal reflowstep establishes an electrical connection between each of internalconductive pads 26 of chip 18 and central part 28 a of crossingconductive strip 28, thus ensuring electrical continuity between each ofthese pads and both ends 28 b at ends 34 of supporting tube 20. Thisheating also allows establishing electrical contact between external pad24 of chip 18 and the conductive material of sleeve 38, for constitutingring electrode 16.

The next step, illustrated in FIG. 5 , is to complete the sealing of theassembly with respect to the external environment, by injecting a massof material 40, such as polyurethane glue, in the space between sleeve38 and central region 30 of supporting tube 20. In addition to sealing,the mass of glue protects the assembly, including chip 18, in respect ofall the constraints and external mechanical stresses, thus ensuring asustainable and protective encapsulation of the assembly of electricaland electronic components, including during the assembly of lead 10 atthe factory.

At this stage, the resulting assembly is ready for a visual inspectionand an electrical test of chip 18 functionalities, prior to assembly ofthe lead body that will now be described.

The next step, shown in FIG. 6 , is to establish electrical connectionsformed by spiral conductors 12, 12 and 14, 14 and to weld theseconductors to corresponding pads 28 b, for example by a weld 42, 42between the stripped end of conductors 12, 12 and end pad 28 b at theproximal side of the crossing conductive strip located there. Welding ispreferably performed by laser welding, and forms no part of the presentinvention. The same welding step is performed in the diametricallyopposite region (not shown in the figure) between conductors 14, 14 ofthe other electrical connection and the other crossing conductive stripdiametrically opposed to that illustrated in FIG. 6 .

The next step, illustrated in FIG. 7 , is to do the same on the oppositeside of annular sleeve 38, i.e., on the distal side, for example by alaser formed weld 44, 44 joining conductors 12, 12 on end 28 b at thedistal side of crossing conductive strip 28 (and similarly forconductors 14, 14 in the diametrically opposed region).

Once welds 42, 42, and 44, 44 are made, the electrical continuity ofconductive connections 12, 12 and 14, 14 is provided on both sides ofsleeve 38. Furthermore, a connection is established, as explained withreference to FIG. 4 , with each of these connections and thecorresponding interior pad of chip 18, for example, as illustrated,between connection 12, 12 and interior pad 26.

The final step, illustrated in FIG. 8 , is to coat or cover spiralconductors 12, 12 and 14, 14 on either side of sleeve 38 with acylindrical isolated sheath 46, for example, made of polyurethane orsilicone, having an essentially constant diameter identical to that ofsleeve 38. This provides a monodiameter lead, having a typical outerdiameter of 1.6 mm (4.8 French), and provided with an internal lumen 22of at least 0.55 mm (also the diameter of the central crossing bore ofsupporting tube 20), similar to conventional leads, such as a XfineTX26D lead manufactured by Sorin CRM, Clamart, France.

By providing one or more supporting tubes 20 interposed betweenconductor sleeves 38 as successive annular electrodes, it is possible tomanufacture a lead comprising at different locations along its length aplurality of electrodes, all multiplexed through a respectivecorresponding chip disposed underneath the electrode.

With reference to FIGS. 9-11 , a second embodiment of the presentinvention is illustrated in which conductive sleeve 38 forming annularelectrode 16 of the first embodiment described above is replaced by aninsulating sleeve 48 of the same diameter, but provided with a pluralityof cavities 50, for example, four axially oriented cavities 50, eachrevealing a conductive pad 24 outside of chip 18. This is realized,instead of a single ring electrode, by a plurality of sector electrodes,for example, oriented in four quadrants, these electrodes beingselectable at will by a multiplexing system integrated into chip 18. Thelatter is provided with a plurality of external conductive pads 24,preferably equal in number to the plurality of sector electrodes, thesepads being still visible in the bottom of cavities 50 of sleeve 48 afterinsertion of sleeve 48 on supporting tube 20 (see FIG. 10 ).

Sector electrodes 52 are preferably formed by clipping a conductormicromechanical component coming into contact with outer conductive pad24 of chip 18 and the outer surface of which (which is flush withcylindrical sleeve 48) is the sector electrode itself.

It will be understood by a person of ordinary skill in the art that itis relatively easy to adjust the surface and shape of each sectorelectrode 50, simply by defining as desired the size and shape of thecavities 50 of insulating sleeve 48.

One skilled in the art will understand the present invention is notlimited by, and may be practice by other than the foregoing embodimentsdescribed, which are presented for purposes of illustration and not oflimitation.

What is claimed is:
 1. A method of manufacturing a lead for an activeimplantable medical device, comprising: providing a supporting tube;disposing a conductive strip on an outer surface of the supporting tubesuch that the conductive strip extends in an axial direction along alength of the supporting tube; mounting a chip including a firstconductive contact pad and a second conductive contact pad to thesupporting tube such that the first conductive contact pad is in contactwith the conductive strip; fitting an electrode to the supporting tubesuch that the electrode is in contact with the second conductive contactpad; coupling a conductor to each end of the supporting tube such thateach of the conductors is in contact with the conductive strip; coveringat least one of the chip and the conductors with a sheath to provide thelead; and separating the sheath into two or more segments by interposingthe supporting tube in the sheath, the two or more segments comprising afirst segment and a second segment.
 2. The method of claim 1, whereinthe supporting tube comprises a central region and two end regions,wherein the central region has a diameter that is greater than adiameter of the two end regions.
 3. The method of claim 2, furthercomprising forming a cavity within the central region of the supportingtube, the cavity forming a chip receptacle configured to hold the chip.4. The method of claim 3, further comprising forming the cavity suchthat a depth of the cavity corresponds with a thickness of the chip suchthat an exterior surface of the chip is flush with the diameter of thecentral region of the supporting tube when the chip is held in thecavity.
 5. The method of claim 3, further comprising forming the chipwith a flexible substrate such that an interior surface of the chip isformed to an outer surface of the supporting tube when the chip is heldin the chip receptacle.
 6. The method of claim 1, further comprisingextending a conductive sleeve circumferentially around a periphery of acentral region of the supporting tube.
 7. The method of claim 6, furthercomprising structuring the conductive sleeve such that the conductivesleeve contacts the first conductive contact pad of the chip when thechip is mounted on the supporting tube.
 8. The method of claim 6,further comprising heating the conductive sleeve onto the supportingtube via thermal reflow to establish electrical continuity.
 9. Themethod of claim 6, further comprising injecting a mass of material in aspace between the conducive sleeve and the central region of thesupporting tube.
 10. The method of claim 9, wherein the mass of materialcomprises a polyurethane glue.
 11. The method of claim 1, wherein thefirst conductive contact pad is positioned on an exterior surface of asubstrate of the chip and the second conductive contact pad ispositioned on an interior surface of the substrate of the chip.
 12. Themethod of claim 1, wherein the conductive strip is a first conductivestrip, the method further comprising disposing a second conductive stripon the outer surface of the supporting tube, wherein the firstconductive strip and the second conductive strip are disposed ondiametrically opposed regions of the supporting tube.
 13. The method ofclaim 1, further comprising defining a plurality of cavities bycircumferentially extending an insulating sleeve around a periphery of acentral region of the supporting tube, wherein the electrode comprises aplurality of sector electrodes, one of each of the plurality of sectorelectrodes disposed with each of the plurality of cavities, wherein thefirst conductive contact pad comprises a plurality of first conductivecontact pads, and wherein each of the plurality of sector electrodes isconnected to a corresponding one of the plurality of first conductivecontact pads of the chip.
 14. The method of claim 1, further comprisingforming the supporting tube of at least one of a ceramic material and aplastic material to electrically isolate the supporting tube.
 15. Amethod of manufacturing a supporting tube of a lead for an activeimplantable medical device, comprising: providing a supporting tube;disposing a conductive strip on an outer surface of the supporting tubesuch that the conductive strip extends in an axial direction along alength of the supporting tube; mounting a chip including a firstconductive contact pad and a second conductive contact pad to thesupporting tube such that the first conductive contact pad is in contactwith the conductive strip; fitting an electrode to the supporting tubesuch that the electrode is in contact with the second conductive contactpad; coupling a conductor to each end of the supporting tube such thateach of the conductors is in contact with the conductive strip coveringat least one of the chip and the conductors with a sheath; andseparating the sheath into two or more segments by interposing thesupporting tube in the sheath, the two or more segments comprising afirst segment and a second segment.
 16. The method of claim 15, furthercomprising extending a conductive sleeve configured as an electrodecircumferentially around a periphery of a central region of thesupporting tube.
 17. The method of claim 16, further comprising forminga cavity within the central region of the supporting tube, the cavityforming a chip receptacle configured to hold the chip.
 18. The method ofclaim 17, further comprising forming the cavity such that a depth of thecavity corresponds with a thickness of the chip such that an exteriorsurface of the chip is flush with the diameter of the central region ofthe supporting tube when the chip is held in the cavity.
 19. The methodof claim 18, further comprising forming the chip with a flexiblesubstrate such that an interior surface of the chip is formed to anouter surface of the supporting tube when the chip is held in the chipreceptacle.